Physiology of interstem dwarfing in apple

147 Pages·2016·4.18 MB·English

Iowa State University Capstones, Theses and
Retrospective Theses and Dissertations
Dissertations
1957
Physiology of interstem dwarfing in apple
Eric Walter Scholz
Iowa State College
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Scholz, Eric Walter, "Physiology of interstem dwarfing in apple" (1957).Retrospective Theses and Dissertations. 2234.
https://lib.dr.iastate.edu/rtd/2234
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PHYSIOLOGY OF INTERSTEM DWARFING- IN APPLE
by
Earl Walter Scholz
A Dissertation Submitted to the
G-raduate Faculty in Partial Fulfillment of
The Requirements for the Degree of
DOCTOR OF PHILOSOPHY
Major Subjects: Horticulture
Plant Physiology
Approved:
Signature was redacted for privacy.
Signature was redacted for privacy.
In Charge of Major Work
Signature was redacted for privacy.
Signature was redacted for privacy.
Heads of Major Departments
Signature was redacted for privacy.
Dean of Graduate7C ollege
Iowa State College
1957
il
TABLE OF CONTENTS
Page
INTRODUCTION 1
REVIEW OF LITERATURE 4
MATERIALS 21
METHODS 23
Growth Measurements 23
Anatomical Studies 24
Experiments with Radioactive Phosphorus 25
Growth Inhibitors of Apple Bark J>0
Treatment of Standard Trees with Antiauxins 40
RESULTS 43
Growth Measurements 43
Anatomical Studies 5°
Experiments with Radioactive Phosphorus ?0
Accumulation of P-^ 70
Downward translocation of P^2 92
Upward movement of p32 99
Growth Inhibitors of Apple Bark 104
Treatment of Standard Trees with Antiauxins 112
DISCUSSION 124
SUMMARY 134
LITERATURE CITED 137
ACKNOWLEDGEMENTS 145
1
INTRODUCTION
Dwarf fruit trees, for hundreds of years popular in
European gardens, are now gaining considerable attention from
horticulturists in America. Not only are they desirable from
the aesthetic viewpoint but because of their diminutive size
they are thought to be ultimately more profitable in the com­
mercial orchard.
Probably one of the most costly operations in commercial
fruit production today is that of spraying; small trees mayb e
more easily and effectively sprayed. Without the necessity
of large ladders, pruning and harvesting operations are facili­
tated, too. Windfall damage is obviously reduced. These facts
justify the renewed interest in dwarf fruit trees.
Apple trees, dwarfed by graftage, mature earlier, usually
bearing their first fruit in three years or less as contrasted
to six to ten years for standard trees. They may tend more to
annual bearing (Banta, 1955b). Their fruits are often larger
and more highly colored than the same variety grown as a
standard tree; it has been claimed, also, that the apples
ripen earlier (Fowler, 1955), but this is not conceded by all.
Higher acre yields have been reported from the few large dwarf
apple orchards now in bearing in the United States.
Dwarf apple trees are not without disadvantages. Chief
among these is their high initial cost. Not only do dwarf
2
trees cost more to propagate, but more must be planted per unit
area. Certain of the rootstocks used are shallow rooted and
trees grown on them must be staked or grown to a trellis. Some
varieties which ordinarily tend to biennial bearing are brought
to annual bearing by being dwarfed, but it is reported by
Fowler (1955) that Starking and Golden Delicious, which are
annual bearing varieties as standard trees, tend to lapse into
biennial bearing when grown as dwarfs.
European dwarf understocks, the Paradise stocks, are
commonly not hardy in the rigorous climate of the midwest;
furthermore, they root poorly at prevailing summer soil tem­
peratures ( Banta, 1955a-, and Nelson and Tukey, 1955)• Mane y
(1943) discovered a more hardy dwarfing stock, which he called
Clark Dwarf, which has greatly alleviated this trouble. The
disadvantage of shallow rooting, necessitating staking and
trellising, has also been obviated by using an interstem of a
dwarfing stock, grafted between a vigorous root and a scion of
the variety in which the dwarfed growth habit is to be induced.
The dwarfing influence may then be derived from this small
section of stem.
The use of dwarfing understocks indicates several possible
physiological influences which might reduce the growth of the
scion, namely: (1) reduced water and mineral absorption, (2)
reduced rate of water and mineral movement or reduced trans­
location of elaborated material, (3) production, destruction
3
or impeded transport of growth regulators, and (4)i ncompatible
graft unions. The employment of a dwarfing interstem, however,
precludes the first possibility as a direct influence.
The induction of dwarfing of apple varieties is only one
of the more prominent manifestations of the intricate inter­
actions between stocks and scions of grafted plants. In an
art so old as graftage it is amazing that so little has been
learned of stock-scion physiology. One is still not able to
predict with accuracy the action of a new stock-scion combina­
tion; only by experience can it be determined what results
will be obtained.
This study was undertaken with the purpose of adding to
our knowledge of graft dwarfing and to investigate the physi­
ological influence of dwarfing interstems.
k
REVIEW OF LITERATURE
Dwarf stocks have been known for over 2000 years.
In the early history of the Greeks, when they were
still in the fruit and not the restaurant busi­
ness, they used dwarf stocks,
wrote T. J. Maney (19^2).
Employment of an interstem section to accomplish the
dwarfing reaction may be a comparatively new process, however.
This method was described in Flora in 1665 by the Englishman,
John Rea:
I have found out another expedient to help them
forward, that is by grafting the Cyen of the
Paradise apple in a Crab, or other Apple-Stock,
close to the ground, with one graft, and when that
is grown to the Bigness of a finger, graft thereon
about eight inches higher, the fruit desired,
which will stop the luxurious growth of the Tree,
almost as well as if it had been immediately
grafted on the forementioned Layers, and will
cause the Trees to bear sooner, more and better
fruits. (Graves, 1950)
Although knowledge of the interstem method was available
in Europe almost 300 years ago, the preponderance of the work
to date has been with dwarfing understocks of the Doucin and
Paradise stocks. This is not unexpected, considering that the
popular Doucin and Paradise dwarfing understocks grow satis­
factorily in the mild climates of England, France,a nd Central
Europe.
In recent years Hatton (1917, 1919) at East Mailing com­
pleted research on the standardization of European dwarf
stocks; various types of the so-called Paradise had been
5
introduced into common use during the seventeenth and eight­
eenth centuries—until no very clear idea was held as to what
these various Paradise stocks were. Duhamel du Monceau in his
Traite des Arbres Fruitiers. 1768, pointed out that in his
comparisons of the Doucin and X^e Pommier nain de Paradis.
degrees of dwarfingness existed (Hatton, 1917). These clonal
rootstocks were studied by Hatton and cooperating workers, and
finally classified with Roman Numerals from I to XVI. They
are now known as East Mailing rootstocks. East Mailing I
(EM I) the Broad-Leaved English Paradise, is slightly dwarfing,
the degree of dwarfing increasing to EM IX, the Juane de Metz
Paradise or Yellow Paradise, which is used as a standard of
comparison of dwarfing today. EM XII and EM XVI and sometimes
EM XIII are considered to be standards of comparison for
vigorous clones or standard trees.
The clonal rootstock, Clark Dwarf, is probably of Paradise
origin. Maney (1942) claims that it is distinct in its charac­
teristics from the standardized English stocks, but that it
undoubtedly originated as a seedling from the old English
Paradise (EM II or EM VII). According to Maney (1943), Iowa
State College acquired dwarf stock In 1924 from H. Walton
Clark, a biologist connected with the United States Bureau of
Fisheries Biological Station at Fairport, Iowa. He had dis­
covered It in the garden of an old lady In Muscatine,I owa.
The tree was 20-25 years old and had experienced temperatures
6
of -25°F without showing signs of injury. According to the
lady, her sailor son had brought the stock from South America.
Karl Erase (1953) compared Clark Dwarf and EM VIII and
found them identical in their characteristics of growth, bark,
internodes, lenticels, leaf blade, base, serrations, petiole,
stipules, and fruit. He claims Clark Dwarf cannot be dis­
tinguished morphologically from the root stock EM VIII and
believed them to be identical.
Early in the nineteenth century, 1816, Thomas Andrew
Knight (1822), first president of the Royal Horticultural
Society of London, discussed the physiology of dwarfing fruit
trees :
Whenever the stick, and graft, or bud, are
not perfectly well united to each other, an
enlargement is well known always to take place
at the point of their junction, and generally to
some extent both above and below it. This is
particularly observable in Peach trees, which
have been grafted at any considerable height from
the ground upon Plum stocks; and it appears to
arise from obstruction, which the descending sap
of the Peach tree meets with in the bark of the
Plum stock, for the effects produced, both upon
the growth and produce of the tree, are similar
to those which occur when the descent of the sap
is Impeded by a ligature, or by the destruction
of a circle of bark. ...The disposition in young
trees to produce and nourish blossom buds and
fruit, is increased by this apparent obstruction
of the descending sap; and the fruit of such young
trees ripens, I think, somewhat earlier than upon
other young trees of the same age, which grow
upon stocks of their own species....
Knight also postulates the same explanation for the
dwarfing effect of the Paradise apple stocks. He thus
7
attributes the dwarfing and early fruiting propensities to the
checking of the flow of nutrient sap to the roots, which deters
vegetative growth, and the resulting accumulation of nutrients
in the tops, which stimulates flowering, fruiting, and hastens
maturity and differentiation; the junction then, accordingly,
is a living, well-controlled girdle.
It is of interest at this point to note Knight's (1824)
hypothesis on the physiological action of a girdle:
According to that hypothesis the true sap of
trees is wholly generated in their leaves, from
which it descends through their bark to the ex­
tremities of their roots, depositing in its course
the matter which is successively added to the
tree ; whilst whatever portion of such sap is not
thus expended sinks into the alburnum, and joins
the ascending current to which it communicates
powers not possessed by the recently absorbed
fluid. When the course of the descending current
is intercepted, that necessarily stagnates, and
it is repulsed, and carried upwards, to be ex­
pended in an increased production of blossoming
and of fruit: and, consistently with these con­
clusions, I have found that part of the alburnum,
which is situated above the decorticated space,
to exceed in specific gravity, very considerably,
that which lies below it. The repulsion of the
descending fluid therefore accounts, I conceive
satisfactorily, for the increased produce of
blossoms, and more rapid growth of the fruit upon
the decorticated branch: but there are other
causes which operate in promoting its more early
maturity. The part of the branch which is below
the decorticated space is ill supplied with
nutriment, and ceases almost to grow; it in con­
sequence operates less actively in impelling the
ascending current of sap, which must also be
impeded in its progress through the decorticated
space. The parts which are above it must there­
fore be less abundantly supplied with moisture;
and drought, in such cases, always operates
powerfully in accelerating maturity.